Tileable Building UV mapping problem
The less planar the shape is in 3D the more distortion their unwrap will result in the UV island. While planning and marking the seams always try to imagine how easy it would be to fold the shape out of paper. After all you can fold a flat shape into 3D cube perfectly, but only if you get the seams right.

That being said if you add seams in the corners of the top part you can get pretty good unwrap results. Here I further corrected some irregularity by first unwrapping all the top row quads without seams and pinning (P key) the straight line in the UV editor to guide the unwrapping algorithm. Taking from here you could also scale the vertical ends to be on same axis if that suits your purpose (better for lightmap, less accurate for texture).



Unwrapping isn't the only option for UVs though. A quick and dirty way to map non-organic shapes with OK results is to use "cube project" or use multiple "project from view" commands. If you got a lot of work to do, you might want to take advantage of this and only bother with more precise and time consuming methods when it makes a big difference.



Learning UV mapping takes time but hopefully this gives you a some initial clue on how unwrapping works.